The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How??? The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.
Quote from: punder on 01/17/2018 05:01 pmThe logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How??? The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.No rocket is pressurized for flight until the final seconds of countdown, as far as I know. So crew weren't working on a pressurized, fueled rocket with either Shuttle or Titan II. There is only head pressure at the bottom of the tanks from the weight of the propellant higher up, but no flight pressurants.AMOS-6 is a pretty good example of why exposure time and risk are not correlated. The LOX tank and the COPVs were being filled, with pressures, fill levels, and temperatures constantly changing until they reached an unstable point that hadn't been reached before, resulting in the explosion. Once filled, everything on a non-sub-cooled rocket is basically in steady state and can sit with occasional topping for boiloff for as long as you want with nothing really changing. This doesn't really work for a subcooled rocket.SpaceX wants to make the process inherently safe and controlled. Every other type of vehicle is fueled with passengers and crew aboard. But they have a lot of work to do to prove that Falcon 9 is just as safe as other vehicles, since the fuels are inherently more dangerous.
Wow this thread is like Deja vu all over again from AMOS-6...
Quote from: Rocket Science on 01/17/2018 07:26 pmWow this thread is like Deja vu all over again from AMOS-6... Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.
Quote from: punder on 01/17/2018 08:09 pmQuote from: Rocket Science on 01/17/2018 07:26 pmWow this thread is like Deja vu all over again from AMOS-6... Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.It's statistical analysis. It's the same reason it's fine for them to store large amounts of fuel and oxidizer on site for months and have people working around them, but why no extraneous personnel can be around when it's transferred from the trucks.
Quote from: punder on 01/17/2018 08:09 pmQuote from: Rocket Science on 01/17/2018 07:26 pmWow this thread is like Deja vu all over again from AMOS-6... Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.Nobody ever said that entering the empty vehicle was more dangerous, the danger is in the fueling process and the question is do you want the crew sitting there during that process.
The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.
Sad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.
So are the Dragon and the Starliner more dangerous for the astronauts to fly in then the Soyuz?
Quote from: Negan on 01/17/2018 09:24 pmSad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6. Lets try and get some numbers. I made some engineering guestimates.Probability vehicle fails after loading = p = 0.01 (an engineering guess upper bound)Probability vehicle fails during loading = 2*p = 0.02 (this is twice more dangerous)Probability escape vehicle fails = q = 0.1 (remember seeing this somewhere)Probability fail to get away from vehicle during fuelling = 2*q = 0.2 (assume twice more dangerous)Number of flight crew = n = 4Number of ground crew = n = 4 (assume same as flight crew)Assume time to load propellants is same as time to load crew (half an hour).Expected loss standard procedure = 2*n*2*q*p = 4*n*p = 0.016Expected loss SpaceX procedure = n*q*2*p = 0.008What this shows is that the SpaceX procedure is safer because less people are exposed to risk and that the crew escape system is safer than having the ground and flight crew try and get away using slide wires. As the Space Shuttle did not have an escape system, the standard procedure is the safest way.